This invention relates to television receivers for high-definition television HDTV) signals.
In a television receiver the greater the number of scan lines in a given frame time (33.3 mS in the U.S. and 40 mS in Europe), the greater the power consumption involved in the magnetic deflection system for the kinescope. In large-screen television receivers for receiving television signals broadcast in accordance with current standards (such as the NTSC standard), so as to use field-to-field line-interlace, an approximation to progressive scan is made by time-compressing the scan lines to half duration and inserting intermediate scan lines generated by interpolation. This procedure doubles the number of scan lines per frame, thereby doubling horizontal and vertical sweep rates and increasing the power consumption of the magnetic deflection system for the kinescope by a factor of four.
High-definition television radio-frequency (RF) signals currently proposed for adoption as a future standard for broadcasting television in the United States are descriptive of digital data. The digital data detected from the HDTV RF signals are descriptions of successive image fields coded essentially in accordance with the MPEG-2 Standard, which descriptions are decoded to recover the raster-scanned video signals. The raster scanning will include a larger number of scan lines than the current NTSC television broadcast standard and may be progressive in nature, rather than line-interlaced as in the current NTSC television broadcast standard. Currently, proposals for 720 progressively scanned scan lines of television image per 60 Hz frame and for 1080 line-interlaced scan lines of television image per 30 Hz frame are being considered. A number of inactive lines must be included in each frame to allow for vertical retrace, so there are totals of about 787.5 lines in the progressively scanned HDTV signal and of about 1125 lines in the line-interlaced HDTV signal. The concerns of the systems designers have been primarily directed to the problems of keeping transmission bandwidth requirements within prescribed limits.
The current standard for HDTV television broadcasting in the UHF television band uses 8-level vestigial sideband (VSB) amplitude modulation of a suppressed-carrier located 310 kHz from the edge of the 6 MHz-wide television channel, and a pilot carrier accompanies the vestigial sideband. Cablecast practice for HDTV television broadcasting is expected to use 16- or 32-state QAM of a mid-channel suppressed carrier, however, with no accompanying pilot carrier. The format for the digital data descriptive of the HDTV display is expected to be the same in cablecast practice as in HDTV broadcasting, or substantially so. The digital data are transmitted in packets, header information in certain of the packets identifying those packets of data that are descriptive of the video portions of a received HDTV program. The digital data are not directly descriptive of the raster scanning of image frames and a digital HDTV receiver generally includes a plurality of dual-ported frame-store display buffer memories, each with a random-access port used for updating the stored image therein and each with a serial output port from which selected lines of data can be read in a shift register operation. Since the luminance signal has more lines per field and has more pixels per scan line than the color-difference signals, the descriptions of the color-difference signals are advantageously stored in dual-ported frame-store buffer memories which are separate from those that store the descriptions of the luminance signals and which are addressed less frequently. During each display field, the ones of these frame-store display buffer memories used for storing descriptions of the current display field in terms of luminance and color-difference video signals supply these descriptions in raster-scan order from their serial output ports.
With the digital standard for broadcasting television in the United States being largely worked out, the time is at hand for considering the problems associated with the commercial production of receivers. Receivers that are capable of receiving transmissions whether in accordance with the former NTSC standard, in accordance with the new digital HDTV broadcast standard, or in accordance with the digital HDTV cablecast practice are desirable. For each individual manufacturer, there are substantial economies associated with the use of similar components across its entire television receiver line. Preferably, a small-screen bottom-of-the-line television receiver with detachable side speakers will use the same digital processing circuitry and buffer memory to generate high-definition luminance and chrominance signals that are used by a top-of-the-line television receiver using a full-wall display unit and a surround-sound speaker system.
When HDTV broadcasts are made, it is likely that some people will desire to receive these broadcasts on small-screen television receivers, some of which will be of portable battery-powered type. The primary interest will be to be able to view video programs transmitted in 16:9 width-to-height ratio. In these small-screen television receivers, the improved spatial and temporal resolution afforded by HDTV transmission will be of no importance at normal viewing distances. Indeed, in kinescopes that use color mask apertures screens, the limitations on smallness of apertures may limit available spatial resolution to less than that broadcast. On the other hand, there is a significant increase in the power consumption in the magnetic deflection system for the kinescope responsive to the faster sweep rates. Since the major portion of the TV receiver power consumption is consumed by the kinescope deflection system, high sweep rates are very disadvantageous in a small-screen TV receiver that is battery-powered. A heavy battery is required if more than a few minutes of viewing time are to be provided before the battery needs to be recharged.
A kinescope which displays a 480-active-scan-line frame with field interlace and with a 16:9 aspect ratio will require nearly twice the deflection power of a kinescope of the same screen height which displays a 480-active-scan-line frame with field interlace and with a 4:3 aspect ratio. The additional power is required for sweeping through the one-third longer scan line in the same scan line period. The deflection angle is related to magnetic field strength and thus to the current in the deflection coils; and the rate of change in the current through the deflection coils depends on the voltage applied thereto. While the horizontal deflection coils are normally resonated to recover energy stored therein, there are I2R losses in the resistance of the deflection coil windings and more significantly there are losses in the deflection amplifiers used to drive the deflection coils which latter losses are related to the square of the driving voltages.
A kinescope which displays a 480-active-scan-line frame scanned in one-thirtieth second with field interlace and with a 16:9 aspect ratio will consume about one-fifth the power of a kinescope of the same screen height which displays a 1080-active-scan-line frame scanned in one-thirtieth second with field interlace and with a 9:16 aspect ratio, however. Not only are horizontal deflection power requirements about one-fifth; so are vertical deflection power requirements. A kinescope which displays a 480-active-scan-line frame scanned in one-thirtieth second with field interlace and with a 16:9 aspect ratio will consume about one-36th the power of a kinescope of the same screen size which displays a 720-active-scan-line progressively scanned (i.e. without field interlace) frame in one-sixtieth second with a 16:9 aspect ratio. Not only are horizontal deflection power requirements about one-36th; so are vertical deflection power requirements. The energy stored in the vertical deflection coils customarily is not recovered by resonating them, owing to the low resonant frequency, so the decrease in vertical deflection power requirement with fewer scan lines is substantial.
A kinescope which displays a 480-active-scan-line frame with a 16:9 aspect ratio and with field interlace in one-thirtieth second will consume a quarter of the deflection power of a kinescope which displays a 480-active-scan-line frame with a 16:9 aspect ratio progressively scanned (i.e. without field interlace) in one-sixtieth second, so the use of field interlace is very desirable in a portable HDTV receiver. In U.S. Pat. No. 5,049,992 issued Sep. 17, 1991 and entitled HDTV SYSTEM WITH RECEIVERS OPERABLE AT DIFFERENT LEVELS OF RESOLUTION Citta et alii describe scan conversion of a 720-active-scan-line frame with a 16:9 aspect ratio progressively scanned in one-sixtieth second to a 480-active-scan-line frame with a 16:9 aspect ratio progressively scanned in one-sixtieth second. Additional measures have to be taken during scan conversion to provide for field interlace, in order to display a 480-active-scan-line frame in one-thirtieth second without excessive flicker owing to motion in the television images.
Conversion of progressive scan video signals of a given frame rate to line-interlaced video signals of a field rate equal to that given frame rate is known per se in the television art. In some television cameras using charge-coupled-device (CCD) images of the field transfer type, the video signals from the cameras are progressive-scan in nature, with 60 (or 50) Hz frame rates, and are converted to line-interlaced video signals by lowpass line-comb filtering with staggered spatial phasing on successive 60 (or 50) Hz frames to generate 60 (or 50) Hz fields of scan lines at halved sweep rates. The lowpass line-comb filtering provides vertical aperture correction that reduces scanning artifacts. In all embodiments of the invention herein described scan conversion is done, not at the television transmitter, but rather at the television receiver.
In certain embodiments of the invention scan conversion to reduce the number of horizontal scan lines per frame and to provide field interlace is done within a television receiver with smaller-size screen, but with the same aspect ratio as the large-size screen of an ordinary HDTV receiver. This scan conversion enables the portable HDTV receiver to use digital processing circuitry similar to that in an ordinary HDTV receiver, while at the same time reducing the sweep rates required in the electromagnetic deflection of the kinescope, thus to conserve power. Display buffer memory similar to that in an ordinary HDTV receiver can be used, with the scan converter including additional buffer memory after the ordinary HDTV receiver display memory. In certain embodiments of the invention this additional buffer memory is reduced to as little as four scan lines of samples for each of the three video signals required to provide a basis for generating a color display. In other embodiments of the invention the need for additional buffer memory is avoided by modifying the display buffer memory from that in an ordinary HDTV receiver, the modification being a banked structuring of the display memory that permits concurrently reading a plurality of scan lines of samples of each video signal to the weighted summation circuitry used for scan conversion.
Even in TV receivers that are powered from the electric mains, there is a desire to keep power consumption low; and, indeed, there is a possibility of limits being placed on the power consumed by home appliances at some future time, in order to contain the costs of power plant construction and maintenance. The use of more than 480 active lines in a kinescope display has other problems besides the increase in power required for deflection. As the number of active lines goes up, the size of the scanning dot must go down in order to utilize the increased display resolution made available. Accordingly, color mask costs go up; and display brightness tends to be reduced, particularly in corners of the screen.
In certain embodiments of the invention scan conversion to reduce the number of horizontal scan lines per frame and to provide field interlace is done within a television receiver having a large-size screen or having a medium-size screen with the same aspect ratio as the large-size screen of an ordinary HDTV receiver. The power consumption associated with deflection is advantageously reduced, but the principal commercial advantage is that dot size can be larger so the display can be made brighter. The brighter display can be better viewed in high ambient light conditions, such as on a porch or in a sun room, for example.
A further aspect of the invention is the scan conversion of NTSC video signals using time compression circuitry to present them in variants of letter-box form in which the images fill the full height of the display screen, but not its full width. It has been proposed to use kinescopes with a compromise aspect ratio between 4:3 and 16:9 width-to-height ratio with NTSC and HDTV signals substantially overscanning the display screen. The inventor believes the commercially correct way to display television images is on a display screen with 16:9 aspect ratio, designed for the new medium that is to supplant the old. The missing xe2x80x9csidesxe2x80x9d of the NTSC display on the display screen with 16:9 aspect ratio makes clear the deficiencies of the old television transmission medium and provides better incentive for transmitter and receiver owners to invest in new equipment. Pix-in-pix displays can be at the side of the NTSC display, and the time compression of each line of NTSC signal can be reduced during the NTSC transmission of widescreen movies.
The various aspects of the invention relate to a television receiver including a kinescope having a display screen with a 9:16 aspect ratio, having phosphors arranged on the back of said display screen with a dot pitch for displaying a 480 scan line frame, and having at least one electron gun for projecting a respective electron beam on the back of said display screen. The kinescope can be of the type having respective electron guns for launching respective electron beams to respectively excite red phosphors, blue phosphors and green phosphors to luminescence. But certain kinescopes for small receivers have only a single electron gun. There is a respective kinescope drive amplifier for each electron gun and deflection circuitry for scanning each electron beam across the back of the display screen of each kinescope used. The scanning is done in a raster scanning pattern with a 9:16 aspect ratio having substantially 240 active lines per field of a two-field frame with the scan lines of the two fields being interlaced with each other.
In one aspect of the invention there is a tuner capable of receiving normal-definition television signals; normal-definition television signal detection circuitry for detecting the raster-scanned video signals contained in the modulation of the normal-definition television signals received by said tuner; horizontal and vertical sync separators for separating normal-definition horizontal and vertical synchronizing pulses from video signals detected by the normal-definition television signal detector; and time compression circuitry for time compressing the normal-definition video signals detected by the normal-definition television signal detection circuitry to generate a respective time-compressed normal-definition video signal for application to each kinescope drive amplifier. The normal-definition horizontal synchronizing pulses are applied to the deflection circuitry to control the beginning of horizontal scanning of the display screen in accordance with the raster scanning pattern; and the normal-definition vertical synchronizing pulses are applied to the deflection circuitry to control the beginning of vertical scanning of the display screen in accordance with the raster scanning pattern.
In another aspect of the invention there is a tuner for receiving high-definition television signals; high-definition television signal decoder circuitry for decoding the raster-scanned video signals digitally encoded in the modulation of the digital high-definition television signals, for providing high-definition-television horizontal synchronizing pulses, and for providing high-definition-television vertical synchronizing pulses for application to said deflection circuitry to control the beginning of vertical scanning in said raster scanning pattern; pulse rate divider circuitry for dividing the rate of said high-definition-television horizontal synchronizing pulses to generate rate-divided high-definition-television horizontal synchronizing pulses occurring at substantially the same rate as normal-definition horizontal synchronizing pulses; and scan converter circuitry responsive to the video signals decoded by the high-definition television signal decoder circuitry to generate a respective scan-converted video signal for application to each kinescope drive amplifier. The rate-divided high-definition horizontal synchronizing pulses are applied to the deflection circuitry to control the beginning of horizontal scanning of the display screen in accordance with the raster scanning pattern; and the high-definition vertical synchronizing pulses are applied to the deflection circuitry to control the beginning of vertical scanning of the display screen in accordance with the raster scanning pattern. Preferably, the high-definition television signal decoder circuitry is of a type that provides indications as to which of a plurality of digital television standards a received high-definition television signal was transmitted in accordance with; and a respective set of vertical scan conversion filters for each of the plurality of digital television standards is included in the high-definition-television scan converter circuitry. A respective set of horizontal decimation filters for each of the plurality of digital television standards can be cascaded before each set of vertical scan conversion filters to reduce the number of samples that need be stored in memory associated with the vertical scan conversion filters.